Could Life Have Come to Earth as an Extremophile?
Cosmic Ancestry is a new hypothesis of the origin of life on Earth. It holds that life on Earth was seeded from space, and that life's evolution to multi-cellular forms depends on genetic material that came from space.
Parallel developments have led to a revival of interest in the possibility that some of the raw materials for life, and possibly even primitive life itself, may have come to the Earth from space. The discovery of increasingly complicated organic molecules between the stars, meteorites, comets, and the atmospheres of the giant planets, has contributed to speculation that the seeds from which terrestrial life grew may have been planted during the early bombardment phase of our planet.
Valuable data bearing on the possible extraterrestrial connection with
life's origin will come from a number of current and planned space missions
designed to collect samples of primitive material from comets and asteroids and
return them for laboratory analysis. Other unmanned probes are scheduled to
explore the environs of the biologically interesting worlds Mars, Europa,
Callisto, and Titan.
In addition, the identification of meteorites that have almost certainly come from the Moon and Mars, has demonstrated that material may be routinely exchanged between worlds as a result of major impacts, giving rise to the possibility of ballistic Panspermia. At the furthest extreme of speculation are the ideas of Hoyle and Wickramasinghe, according to which primitive organisms may actually have evolved in space.
Finally, life seems to have taken hold so quickly! Almost as soon as life *could* exist, amidst the bombardment of enormous asteroids, it did. See here or here for a full discussion of this idea. Did life form quickly because it didn't have to start from scratch, but instead came to the Earth on a cosmic coach?